The distribution of corticotropin-releasing factor immunoreactive neurons and nerve fibres in the brain of Gambusia affinis and Salmo trutta.

The study was carried out on the distribution of neurons and fibres which contain the Corticotropin releasing factor-like (CRF) immunoreactivity in the encephalon of two species of teleosts, Gambusia affinis and Salmo trutta. The peroxidase-antiperoxidase (PAP) immunocytochemical technique was employed. The present study has shown differences between both species. In Gambusia affinis, positive neurons were observed in the area ventralis telencephali pars lateralis (VLT), in the nucleus praeopticus (NPO) and in the nucleus lateralis tuberis (NLT). The immunoreactive fibres were in the area ventralis telencephali, in the preoptic hypophyseal tract and in the hypophysis. In Salmo trutta the immunoreactive cells were seen in the pars magnocellularis and pars parvocellularis of the NPO and in cerebrospinal fluid (CSF) contacting neurons of the NLT. The pattern of distribution of immunoreactive fibres in Salmo trutta was different from that in Gambusia affinis. In addition to the distribution of perikarya in Gambusia affinis (in the VLT and in the preoptic hypophyseal tract), fibres were also observed in the tubero-hypophyseal tract and in the posterior hypothalamus. The hypophysis of Salmo trutta also presents an extensive labelling. The interspecific differences shown in the present study should be due to the different degree of evolution in the two species studied and to other causes, such as environmental ones.

Distribution of neuropeptide Y-like immunoreactivity in the brain of Salmo salar and Gambusia affinis.

Through the immunohistochemical PAP technique, the distribution of immune positive neurons and fibres for an antibody anti-NPY in the encephalon of salmon fixed in Bouin have been located and studied. NPY-positive neurons are found forming three important nuclei: in the ventrolateral telencephalon; in the tegmentum mesencephali; and in the locus coeruleus. Neurons in the optic tectum, in the thalamic region and a few in the preoptic recess have also been located. The fibres were found throughout the brain, with the exception of the cerebellum, presenting a greater density in three regions: in the dorsal telencephalon; in the mesencephalon; and in the visceral lobes in the rhombencephalon. With the aim of proving if this distribution is found in other groups of teleosts, we processed, with the same technique, the advanced teleost Gambusia affinis, in order to compare it with the primitive teleost Salmo salar. The results show that in both fish this neuropeptide has the same pattern of distribution. The results also suggest that in fish this neuropeptide can be involved in several functions of the central nervous system, as has been demonstrated for mammals. The innervation of the visceral lobes and also the presence of NPY-fibres in the posterior hypothalamus are anatomical supports of the studies which suggest that NPY is related to the control of the food intake.

Hindbrain floor plate of the rat: ultrastructural changes occurring during development.

Most of the molecular and experimental studies on the floor plate (FP) have been performed on the FP region extending along the spinal cord. However, little is known about the hindbrain FP. The FP undergoes regional and temporal changes throughout development, but information with respect to the ultrastructural correlate of such changes is missing. The present investigation was focused on the ultrastructural developmental changes occurring in the FP of the rat hindbrain. The FP cells of the hindbrain secrete a material reacting with antibodies against the secretory glycoproteins of the subcommissural organ (AFRU). This antibody was used to perform an ultrastructural immunocytochemical analysis of the rat FP. From E-12 on, there is a progressive increase in the development of the rough endoplasmic reticulum (RER), so that by E-18, it has reached a high degree of hypertrophy. A unique feature of the hindbrain FP cells is the presence of tubular formations and 140-nm vesicles that appear to originate from RER cisternae. The labelling of these two structures with AFRU and Concanavalin A strongly suggests that they are pre-Golgi compartments containing secretory material. Since these structures are present in the basal process and in the apical cell pole of the FP cells, the possibility that they release their content at these sites, is discussed. It is proposed that a secretory mechanism bypassing the Golgi apparatus (constitutive secretion?) operates in the FP cells. The presence of apoptotic cells within the FP of E-20 embryos and newborns suggests that death, and not re-differentiation, is the fate of the FP cells.

Cell types of the third ventricle wall of the rabbit (Oryctolagus cuniculus).

A comparative study using optical and electron transmission and scanning microscopes was carried out to determine the cells that comprise the wall of the third ventricle of the rabbit (Oryctolagus cuniculus). Three cell types have been distinguished: type I cells are the most numerous and may present a flat, cubical or cylindrical aspect, with cilia and microvilli at their apical end. Type II cells have an irregular elongated morphology, lack cilia on their luminal end and show functional characteristics of secretory cells. Type III cells are also elongated, and bear irregular protrusions at the apical end. A long process at the basal end of these cells goes deep into the neuropil and becomes related with neurons or blood vessels; these correspond to tanycytes.

Supraependymal cell clusters and invaginations in the epithalamic third ventricle of the rabbit (Oryctolagus cuniculus).

Supraependymal cell clusters and deep invaginations of the ependymal wall, situated in the epithalamic area of the third ventricle of the rabbit have been precisely located by means of semithin serial sections. A study of these structures has been carried out using optical transmission and scanning electron microscopy. The round shaped supraependymal cell clusters revealed two types of cells: type I, of central location and bearing the morphological features of neurons and type II, located peripherically and of possible ependymary origin and nature. In the same epithalamic region, deep invaginations of the ventricular wall, lined by ependymal cells of similar morphology to those coating the rest of the third ventricle, are described. The functional role of both structures is discussed.

Ultrastructural study of the cellular components of the organum vasculosum lamina terminalis of the rabbit (Oryctolagus cuniculus).

We studied the organum vasculosum of the lamina terminalis (OVLT), under the electron microscope (transmission and scanning) to determine its ultrastructural features. Two cell types are differentiated. Type I cells are typical ependymal cells bearing few cilia. Type II cells present a tanycytic morphology. The latter present a long basal process which travels from the perikarya and intermingles with other neuronal components, finally reaching the perivascular spaces where it comes into close contact with fenestrated capillaries.

The metencephalic floor plate of chick embryos expresses two secretory glycoproteins homologous with the two glycoproteins secreted by the subcommissural organ.

The nature and the function of the compounds secreted by the floor plate (FP) of the metencephalon are little known. The FP cells of the hindbrain react with antibodies (AFRU) against the glycoproteins secreted by the subcommissural organ (SCO). One of the these proteins, RF-Gly I, is a 540-kDa core glycosylated protein. The aims of the present investigation were to identify by immunoblot the AFRU-immunoreactive compound secreted by the FP of chick embryos, to establish temporal and regional patterns of this secretory activity, and to obtain information about the fate of these compounds. It was established that the SCO and FP of chick embryos secrete two AFRU-immunoreactive compounds of 540 and 230 kDa. The two compounds secreted by the FP have been designated as FP-Gly I and FP-Gly II. The expression of these proteins was circumscribed to the metencephalic FP, and occurred from HH 29 to HH 36. Within the FP cells, FP-Gly I and FP-Gly II were confined to the supranuclear and apical regions, which under the electron microscope displayed numerous cisternae of the rough endoplasmic reticulum and granules. Aggregates of AFRU-immunoreactive material appeared on the free surface of the FP. The possibility that FP-Gly I and FP-Gly II are released into the ventricle to reach distant targets is discussed.